The present invention relates in general to an electrical safety fuse and in particular to a high voltage, high power fuse of the type which includes a main fusible wire for interrupting a short-circuit current in an outer circuit, an auxiliary fusible wire for releasing a spring biased impact pin, an insulating body surrounding the two fusible wires and being hermetically closed at two opposite sides thereof by conductive caps, the caps acting as contact terminals for the two fusible wires.
High voltage, high power (HRC) fuses of this kind are devices for a singular interruption of short circuit currents in interior and exterior switching installations. These fuses are suitable as a short-circuit protection of voltage converters, capacitors, cable distributors, transformers and the like. They protect the series connected apparatuses and conductors against thermal and dynamic effects of excessive short-circuit currents. Current limiting fuse of this kind interrupts such currents already in the course of their increase.
The HRC-fuses serve only as a protection against short-circuit, the protection against overload is performed by other current safety devices at the secondary side (low voltage side). During the failure of these secondary sides overcurrent protecting devices or in the case of a failure of the interconnected devices such as for example distributing transformer, a hazardous gap occurs in the overall protection range inasmuch the conventional HRC-fuses cannot interrupt currents whose value is below the triple nominal value of the fuse. In order to eliminate this safety gap, the so-called full range fuses have been recently developed, all representing a combination of a HRC-fuse with an overload fuse. This known compound device, however, is very expensive.
In order to connect the distributing transformers to an intermediate voltage network, there are often used load interrupting switches in combination with HRC-fuses. The load interruption switches reliably respond to currents below the triple value of nominal value of the fuse.